Suppression of interference fading in φ-OTDR based on FDM and dual RVS

Abstract

Phase-sensitive optical time-domain reflectometry (φ-OTDR) is highly sensitive to strain changes of sensing fiber caused by external vibration, by which we are able to locate the vibration. In practice, interference fading will inevitably occur in backscattered Rayleigh traces of φ-OTDR due to the use of highly coherent light source, which increase the possibility of failure detection. In order to reduce the influence of interference fading on vibration detection, both frequency-division multiplexing (FDM) and rotated-vector-sum (RVS) over both time-and frequency-domain are employed in our method. Based on the method, we perform φ-OTDR experiment to locate vibrations. By extracting 3 frequency components of the beating signals (~200 MHz) and carrying out dual rotation, interference fading can be suppressed to a large extent, the vibration-induced phase changes are precisely recovered. One point should be noted is that we found that there is a certain correlation between each frequency component extracted from the beating signal, resulting in interference fading points cannot be completely removed.